Color display system



April 15, 1969 s. R. SHORTES COLO R DISPLAY SYSTEM Sheet Filed May 31. 1966 FIGI.

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April 15, 1969 s; R. SHO'RTES 3,439,217

COLOR DISPLAY SYSTEM Filed May 31. 1966 Sheet 1 of 2 FIGZ;

United States Patent Office 3,439,217 Patented Apr. 15, 1969 US. Cl. 315-14 5 Claims ABSTRACT OF THE DISCLOSURE This specification discloses a color display system, characterized by a screen including phosphors which emit light of different colors when struck by electrons of different energies and including an electron permeable conductive film, a single electron gun for emitting a beam of electrons toward the screen, field generating means for deflecting the beam of electrons in a scanning raster, a generally annular electrode concentric with the gun and axially displaced therefrom toward the screen and into the region of the field produced by the field generating means, means for applying D.C. bias voltage to the screen and to the electrode to accelerate the electrons emitted from the gun toward the screen, and means for applying a first time varying voltage of a first phase to the annular electrode, in response to a first triggering signal, and for simultaneously applying a second time varying voltage of opposite phase to the conductive film of the screen and for reversing the phases of the first time varying voltage and the second time varying voltage in response to a second triggering signal.

This invention relates to a color display system and more particularly to such a system which produces multiple color images having color image components which are in substantial registration.

Various kinescope color display systems have been proposed in which electrons of different energies are employed to produce light of different colors. These known systems typically employ a phosphor screen including a plurality of phosphors which emit light of different colors when struck by electrons having different energies. One problem with this type of display system is that it is difficult to scan the screen uniformly with the electrons of differing energies, since the higher energy electrons are less subject to deflection by the magnetic or electric fields conventionally employed to sweep a beam of electrons in a raster over a phosphor screen than the lower energy electrons. Thus, if this difference in deflection is not compensated for, misregistration will result.

Among the several objects of the present invention may be noted the provision of a color display system which produces multiple-color images having color image components which are in substantial registration; the provision of such a system in which the energy of an electron beam is varied to produce light of different colors on a screen including a plurality of phosphors which emit light of different colors when struck by electrons of dif ferent energies; the provision of such a system which requires only a single electron gun; the provision of such a system which is reliable and which is relatively simple and inexpensive. Other objects and features will be in part apparent and in part pointed out hereinafter.

Briefly, a color display system of this invention includes a screen having phosphors which emit light of different colors when struck by electrons of different energies. A single electron gun emits a beam of electrons toward the screen. Field generating means are provided for deflecting the beam of electrons in a scanning raster. A generally annular electrode is positioned concentric with the gun and is axially displaced therefrom toward the screen and into the region of the field produced by the field generating means. D.C. bias voltages are applied to the screen and to the annular electrode to accelerate electrons emitted from the gun toward the screen. Outof-phase, time-varying voltages are applied to the screen and to the annular electrode thereby to accelerate electrons emitted from the gun to at least two different energies for energizing the screen to produce multiplecolor images having color image components which are in substantial registration.

The invention accordingly comprises the constructions hereinafter described, the scope of the invention being indicated in the following claims.

In the accompanying drawings, in which several of various possible embodiments of the invention are illustrated,

FIGURE 1 is a partially schematic diagram of a color display system of this invention; and

FIGURE 2 is a similar diagram of a modification of this color display system.

Corresponding reference characters indicate corresponding parts throughout the several views of the drawmgs.

Referring now to FIGURE 1, there is indicated at 11 a color kinescope constructed according to the present invention. Kinescope 11 includes a conventional glass envelope 13 having a screen portion 15, a neck portion 17 and a generally bell-shaped intermediate portion 18 connecting the neck and screen portions. Coated on the inner surface of the screen portion 15 is a phosphor layer 19 which includes phosphors which emit light of different colors when struck by electrons of different energies. Phosphor screen 19 may, for example, be constituted by a mixture of two different kinds of phosphor particles one of which emits red light when energized by electrons having energies above a relatively low predetermined level and the other of which emits cyan light when energized by electrons having energies above a relatively high predetermined level. Such a screen will emit red light when struck by electrons at the relatively low level and will emit white or substantially achromatic light when struck by electrons at the relatively high energy level, which electrons can energize both of the phosphors. Such red-white image displays are known in the art for the presentation of color images and images so presented appear to have a relatively wide range of hues subjectively having a greater saturation than that which is actually present in the colorimetric sense. Methods of preparing phosphors useful in the present invention are disclosed in my copending application Ser. No. 459,582, filed May 28, 1965, entitled Phosphors for Color Display System.

Over phosphor screen 19 is deposited a film 21 of aluminum which is conductive and yet is also thin enough to be substantially electron permeable. By means of film 21 suitable electron accelerating voltages may be applied to the phosphor screen 19. Aluminum film 21 also extends beyond the face portion 15 of kinescope 11 onto a preselected margin of the intermediate portion 18 of envelope 13 thereby constituting a first conductive band 23 on the intermediate portion.

Within the neck portion 17 of envelope 13 there is mounted a conventional electron gun 27 for emitting a beam of electrons directed toward phosphor screen 19'. For the purpose of the example described herein, it is assumed that this color display system is operated in a line sequential mode. For this purpose a line sequential, color video signal is applied to gun 27 for varying the electron beam current, that is, the rate at which electrons are emitted by the gun. The video signal thus controls the instantaneous brightness of the light produced by the beam on phosphor screen 19. It should be understood,

however, that a dot sequential or field sequential presentation of the different colors may also be employed by appropriately varying the different switching rates described hereinafter and applying a corresponding video signal to gun 27.

Electrons emitted from gun 27 pass through the magnetic influence of a deflection yoke 29. Yoke 29 is energized in conventional manner to deflect the beam of electrons in a scanning raster over the envelope face portion 15. However, as is understood by those skilled in the art, the raster will be of uniform size only if the electrons emitted by gun 27 are all accelerated to the same energy or if compensation is made for the different deflection effects experienced by electrons having different energies.

The inner surface of the part of the intermediate envelope portion 18 adjacent neck 17 is coated with a conductive band as indicated at 33 thereby to constitute a generally horn-shaped electrode which is concentric with gun 27 and through which the beam of electrons emitted by the gun pass on their way to phosphor screen 19. Band 33 may conveniently be constituted by a so-called dag coating on envelope 13. As is explained in greater detail hereinafter, electrode band 33 is employed to exercise a radial corrective effect on the deflection of the electron "beam passing therethrough. Electrical connections are made to the electrode band 33 and to the phosphor screencovering aluminum film 21 as indicated at 37 and 39 and these connections extend through envelope 13 by means of conventional feed-through terminals (not shown). Respective D.C. biasing potentials are applied to electrode band 33 and to the screen 19 through inductors L1 and L2 which serve to effectively block AC. or time-varying voltages as explained hereinafter. Appropriate nominal D.C. potentials for electrode 33 and screen 19 are approximately 12 and 16 kilovolts, respectively.

On the outside of the intermediate portion 15 of envelope 13 there is deposited a band 37 of conductive aluminum film in juxtaposition with band 33. Band 37 is thus spaced substantially equidistantly outwardly from electrode band 33 and is thus capacitively coupled to it through the glass envelop 13. A similar aluminum band 39 is deposited on the envelope 13 in juxtaposition with the marginal band 23 of the aluminum film covering phosphor screen 19. Aluminum band 39 is thus capacitively coupled to the screen 19 through the glass envelope 13.

Aluminum bands 37 and 39 are provided with out-ofphase time-varying voltages, and in particular with voltage waves of rectangular waveform and of several kilovolts amplitude, by the circuit indicated generally at 41. Other known circuits for generating such waveforms may also be used. Bands 37 and 39 are connected to the opposite ends of the secondary winding W2 of a transformer T1. Winding W2 includes an intermediate tap TP which is connected to ground. Transformer T1 also includes a primary winding W1, one end of which is connected to ground through the anode-cathode circuit of an SCR (silicon controlled rectifier) Q1. Triggering signals applied to a terminal 43 are coupled to the gate terminal of SCR Q1 through a coupling capacitor C1. The other end of wind ing W1 is connected to a positive supply terminal 45 through a DC. blocking capacitor C2 and a current limiting resistor R1. The voltage existing between capacitor C2 and resistor R1 is smoothed by a filter capacitor C3. Primary winding W1 and capacitor C2 together are shunted by the anode-cathode circuit of a second SCR Q2. Triggering signals for SCR Q2 applied to a pair of terminals 47 and 49 are coupled to the gate-cathode circuit of the SCR by a transformer T2.

The operation of circuit 41 is explained in greater detail in copending application Voltage Switching Apparatus For Color Kinescopes, Ser. No. 553,946, filed May 31, 1966, by William H. Clingman, Jr. and assigned to the assignee of the present application. For the purpose of the present invention, however, the following brief explanation of its operation is sufficient.

When SCRs Q1 and Q2 are triggering alternately, a voltage of rectangular waveform is applied to each of the bands 37 and 39, the two signals being out-of-phase with respect to ground potential. The rectangular waveforms applied to bands 37 and 39 are capacitively coupled to the electrode band 33 and to the screen 21 respectively. These waveforms are, however, effectively blocked from the DC. sources biasing these elements by the chokes L1 and L2 as noted previously. Electrons emitted by gun 27 during the different time intervals corresponding to the two different voltage levels of the rectangular waveform are thus accelerated to different energy levels before reaching phosphor screen 19. The energy levels are adjusted in relation to the characteristics of the phosphors which make up screen 19 so that the lower energy electrons excite only the red phosphor while the higher energy electrons excite both the red and cyan phosphors thereby causing white light to be emitted.

The frequency of the rectangular wave is adjusted and synchronized so that the different accelerating voltages are produced during periods which correspond to the sequencing of the color video signal applied to gun 27. The beam current is thus modulated to reproduce the various image components in their respective colors. In the example illustrated this is assumed to be at a line sequential rate.

The color display system illustrated in FIGURE 1 is operated to produce color images having component color images which are in substantial registration as follows, a red-white, line sequential mode of operation being assumed. At the start of a white line, SOR Q1 is triggered so that the aluminum band 39 is driven positive with respect to ground. Because of the capacitive coupling between this band and the aluminum layer 21, the screen 19 is driven to the higher of its two potentials and electrons emitted from gun 27 are accelerated to a relatively high energy level. These electrons thus produce white light when they strike phosphor screen 19 as explained previously. As the band 39 is driven to a positive voltage, the band 37 is driven to a negative voltage and thus the electrode 33 is capacitively driven to the lower of its two voltage levels. Accordingly, electrons emitted from gun 27 are not greatly accelerated as they first leave the gun but rather attain only a relatively low velocity in the region of the yoke 29. These electrons 'are thus relatively highly subject to deflection by the yokes field and therefore follow a path having an early high curvature as represented at A in FIGURE 1. As these electrons leave the vicinity of electrode 33, however, they are subjected to a relatively intense electric field and are thus accelerated to approach screen 19 at a relatively steep angle, impinging at a point indicated at C.

When a red line is to be displayed, the SCR Q2 is triggered and the aluminum band 39 is driven negatively with respect to ground. The screen 19 thus assumes the lower of its two voltage levels. The total acceleration experienced by electrons emitted by gun 27 is then relatively small and only the red phosphor is energized.

Simultaneously with the application of the negative voltage to aluminum band 39, a positive voltage is applied to band 37 so that the electrode 33 is capacitively driven to the higher of its two voltage levels. Electrons emitted from gun 27 during this period are thus rapidly accelerated as they first leave the gun and thus are not greatly deflected by yoke 29. These electrons thus follow a path substantially as indicated at B in FIGURE 1. As the screen 19 is then at the lower of its two potentials, these electrons are not further greatly accelerated and therefore approach the screen substantially at the angle determined by their earlier deflection, striking the screen substantially at the same point C as the higher energy electrons following the path A.

As the particular configuration of the kinescope 11 will affect the distribution of the electric fields within the kinescope, as will be boundaries of the electrode band 33 and the aluminum screen coating 21, it may be seen that the particular :DJC. biasing voltages and rectangular wave amplitudes which must be applied to achieve best registnation will vary from tube to tube. Typically the rectangular waves coupled to the focusing electrode and to the screen will have to be of somewhat different amplitudes, the intermediate tap TP being shown off-center in FIGURE 1 for this reason.

In FIGURE 2 there is illustrated a modification of the kinescope of this invention, which modification employs a horn-shaped elctrode 63 which is separate from the tube envelope and may therefore be contoured independently thereof. Electrode 63 is mounted coaxially with gun 27 and spaced therefrom toward the phosphor screen 19. In this embodiment also an aluminum layer is deposited over screen 19 for applying suitable accelerating votages thereto. Electrode 63 and aluminum layer 21 are each directly connected to one end of a respective secondary winding W5 and W6 of a transformer T3. Transformer T3 includes a primary winding W7 which is adapted to be driven by a suitable rectangular w ave generator such as the circuitry illustrated in FIG- URE 1. The opposite ends of the secondary windings W5 and W6 are connected to appropriate DC. biasing potential sources as indicated.

When the primary winding W7 is driven by a rectangular wave, the electrode 63 and the screen 19 are each thus switched between two respective voltage levels in a manner substantially similar to the electrode 33 and screen 19 shown in FIGURE 1. While this construction does away with the need for the chokes L1 and L2 and for the construction of the coupling capacitances which feed the rectangular wave through the kinescope envelope 13, it does require that the windings W5 and W6 be insulated to withstand the relatively high D.C. biasing potentials applied thereto.

In operation, the electrode 63 tends to reduce the acceleration of electrons emitted by gun 27 in the region of the yoke when the screen 19 is at its higher potential and to produce a relatively high early acceleration of the electrons when the screen is at its lower voltage thereby causing electrons having different energies to experience the same total deflection before reaching the screen in the same manner as the embodiment illustrated in FIGURE 1.

The present invention may also be employed to obtain proper registration of color image components in a threecolor display system in which case out-of-phase timevarying voltages having three discrete steps may be applied to the compensating electrode and to the phosphor screen.

In view of the above, it will be seen that the several objects of the invention are achieved and other advantageous results attained.

As various changes could be made in the above constructions without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. A color display system comprising:

a screen including a plurality of phosphors which emit light of different colors when struck by electrons of different energies and an electron permeable conductive film;

a single electron gun for emitting a beam of electrons toward said screen;

field generating means for deflecting said beams of electrons in a scanning raster;

a generally annular electrode concentric with said gun and axially displaced therefrom toward said screen and into the region of the field produced by said field generating means;

means for applying DC. bias voltages to said conductive film of said screen and said electrode to accelerate electrons emitted from said gun toward said screen; and

means for applying a first time varying voltage of a first phase to said annular electrode and for simultaneously applying a second time varying voltage of phase opposite to said first phase of said first time varying voltage to said conductive film of said screen to accelerate said beam of electrons to a first energy level in response to a first trigger signal and energize part of said phosphors to produce first color image components and for reversing the phases of said first time varying voltage and said second time varying voltage in response to a second triggering signal and accelerate said electrons toward said screen to a second energy level and energize a part of said phosphors to produce second color image components which are in in substantial registration with said first color image components.

2. A color display system as set forth in claim 1 wherein said gun and said screen are supported within a kinescope envelope and wherein said electrode is a metal element mounted within said envelope coaxially with said gun.

3. A color display system as set forth in claim 2 wherein said electrode is generally horn-shaped.

4. A color display system as set forth in claim 1 wherein said gun and said screen are supported wit-bin a kinescope envelope and wherein said electrode comprises a conductive coating on the inner surface of said envelope adjacent said gun.

5. A color display system as set forth in claim 1 wherein said film extends beyond said screen over portions of said envelope adjacent thereto.

References Cited UNITED STATES PATENTS 2,741,526 4/1956 Laiferty 315-14 3,005,927 10/1961 Godfrey 31376 X 3,109,956 11/1963 Stratton 31514 3,114,795 12/1963 Moles 315-44 X 3,225,238 12/196 Feldman 313-92 3,290,435 12/1966 Shimada 315l4 RICHARD A. FARLEY, Primary Examiner.

MALCOLM F. HUBLER, Assistant Examiner. 

